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Population abundance of rhizobia nodulating cowpea in major production areas of Ethiopia as influenced by cropping history and soil properties

ABSTRACT: The size of the native rhizobia population is the most prevailing ecological factors that regulate the competitive success of inoculated rhizobia. Although soil may contain a considerable size of native rhizobia population, the abundance of rhizobia found in a particular soil should be enumerated. This will help to know the sufficiency of the rhizobia for nodulation and successful nitrogen fixation which is offer input in agricultural systems to withstand long-standing soil fertility. Besides, a variety of biotic and abiotic factors such as host plant, cropping history, and soil physico-chemical properties are known to affect rhizobial population in the soil. This study determined the size of the native population of rhizobia nodulating cowpea isolated from selected major growing areas of Ethiopia and revealed how the population relates to cropping system and physicochemical soil parameters at the collection sites. The enumeration study of native rhizobial population revealed that the population size of native rhizobia compatible to cowpea is high in cowpea producing areas of Ethiopia ranging from 3.1x104 to 1.0x107 rhizobia cells g-1 of soil and the population varied at various locations. There was no significant correlation between all soil factors (pH, total N, and available P) and the number of rhizobia populations harbored in tested soils. All the soils used for the study had been cropped with cowpea either in monoculture (sole cowpea), intercropping (mostly with sorghum and maize) and crop rotation for many years. These indicates that populations of cowpea nodulating rhizobia in soil strongly depend on cultivation of their host plant. These results lead to suggest that the soils of major cowpea growing areas of Ethiopia had adequate levels of rhizobia capable of nodulating and adequate to give satisfactory nitrogen fixation and nodulation on cowpea.

SUBMITTER: Erana Kebede

PROVIDER: S-BSST411 | biostudies-other |

REPOSITORIES: biostudies-other

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Project description:The structure of rhizobial communities nodulating Acacia in southeastern Australia from south Queensland to Tasmania was investigated by a molecular approach. A total of 118 isolates from nodule samples from 13 different Acacia species collected at 44 sites were characterized by small-subunit (SSU) ribosomal DNA (rDNA) PCR-restriction fragment length polymorphism analysis. Nine rhizobial genomospecies were identified, and these taxa corresponded to previously described genomospecies (B. Lafay and J. J. Burdon, Appl. Environ. Microbiol. 64:3989-3997, 1998). Eight of these genomospecies belonged to the Bradyrhizobium lineage and accounted for 96.6% of the isolates. The remaining genomospecies corresponded to Rhizobium tropici. For analysis of geographic patterns, results were grouped into five latitudinal regions regardless of host origin. In each region, as observed previously for rhizobial isolates taken from non-Acacia legumes (Lafay and Burdon, Appl. Environ. Microbiol. 64:3989-3997, 1998), rhizobial communities were dominated by one or two genomospecies, the identities of which varied from place to place. Despite this similarity in patterns, the most abundant genomospecies for Acacia isolates differed from the genomospecies found in the non-Acacia-derived rhizobial collection, suggesting that there is a difference in nodulation patterns of the Mimosoideae and the Papilionoideae. Only two genomospecies were both widespread and relatively abundant across the range of sites sampled. Genomospecies A was found in all regions except the most northern sites located in Queensland, whereas genomospecies B was not detected in Tasmania. This suggests that genomospecies A might be restricted to the more temperate regions of Australia, whereas in contrast, genomospecies B occurs in different climatic and edaphic conditions across the whole continent. The latter hypothesis is supported by the presence of genomospecies B in southwestern Australia, based on partial SSU rDNA sequence data (N. D. S. Marsudi, A. R. Glenn, and M. J. Dilworth, Soil Biol. Biochem. 31:1229-1238, 1998).

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Population abundance of rhizobia nodulating cowpea in major production areas of Ethiopia as influenced by cropping history and soil properties

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